Early and late functions associated with the Golgi apparatus reside in distinct compartments.
Enzymes that catalyze the two successive stages of Golgi-associated processing of asparagine-linked oligosaccharides distributed differently when membranes from Chinese hamster ovary cells were centrifuged in a sucrose density gradient. A mannosidase that removes only outer, alpha-1,2-linked mannose residues from the precursor oligosaccharides of the vesicular stomatitis viral G protein (to yield a "trimmed" oligosaccharide core) was separated from enzymes (galactosyl- and sialyltransferases) that act in the later, terminal stage of glycosylation. Freshly acylated G protein with newly trimmed oligosaccharides banded in the distribution of early-acting membranes, defined by the mannosidase, whereas G protein pulse-labeled with [3H]galactose distributed in the profile of the late-acting membranes. G protein present in the early-acting membranes in crude fractions could be terminally glycosylated by incubation with exogenous Golgi membranes in vitro; G protein lost its ability to be processed in vitro as it appeared to enter the late-acting membranes in vivo. These experiments reveal the existence of two distinct compartments through which intracellularly transported proteins such as G pass in sequence as Golgi-associated processes are carried out. It is likely that these compartments consist of cisternae on the cis and trans sides of the Golgi stack.
D000818:Animals; D006224:Cricetinae; D003412:Cricetulus; D005260:Female; D005700:Galactosyltransferases / Q000378:metabolism; D006023:Glycoproteins / Q000378:metabolism*; D006056:Golgi Apparatus / Q000502:physiology* / Q000648:ultrastructure; D007739:L Cells; D008361:Mannosidases / Q000378:metabolism; D051379:Mice; D008970:Molecular Weight; D014764:Viral Proteins / Q000378:metabolism
D006023:Glycoproteins; D014764:Viral Proteins; D005700:Galactosyltransferases; D008361:Mannosidases